Add mark size for legends

Author: JasonGross

src/tikzplotlib/_legend.py

@@ -61,6 +61,23 @@ def draw_legend(data, obj):
     if fill_xcolor != "white":  # white is default
         legend_style.append(f"fill={fill_xcolor}")
 
+
+    mark_options = []
+    handles = obj.legendHandles if hasattr(obj, "legendHandles") else obj.legend_handles if hasattr(obj, "legend_handles") else None
+    if handles:
+        all_sizes = set(sz for handle in handles for sz in handle.get_sizes())
+        if len(all_sizes) > 1:
+            warnings.warn(f"Varying marker sizes in the legend: {all_sizes}. Ignoring all of them.")
+        elif all_sizes:
+            mark_size = all_sizes.pop()
+            ff = data["float format"]
+            # setting half size because pgfplots counts the radius/half-width, and sqrt the area
+            pgf_size = 0.5 * mark_size ** 0.5
+            mark_options.append(f"mark size={pgf_size:{ff}}")
+
+    if mark_options:
+        legend_style.append(f"mark options={{{', '.join(mark_options)}}}")
+
     # Get the horizontal alignment
     try:
         alignment = children_alignment[0]